The invention relates generally to data base systems and in particular to multi-user concurrent transactional processing systems and methods.
It is common in a transactional system employing a data base file to create, in a local memory, a "before-image" representing each file entry as it existed before a transaction or processing update has occurred, and to further store an "after-image" representing the status of the file entry after the transaction or processing update has occurred. These images are important for recreating the contents of the file in the event that the file is destroyed, for example by a disk crash. Typically the after-images are generated and stored temporarily in a local after-image memory file until the after-image file is full. Then, a user must manually save the after-image file by storing it on a tape or disk file which will act as a permanent storage. During the save process, all other processor functions, including transactional processing, must be stopped. There results, therefore, an undesirable interruption in transaction processing which reduces efficiency and throughput in the system.
It is therefore an object of the invention to increase throughput in a data base processing apparatus and method which employs after-imaging. Another object of the invention is a high reliability data base processing system wherein permanent after-image records can be attained without interrupting the normal run processing of the system and without compromising the reliability and effectiveness of the after-imaging method and apparatus.